1. Field of the Invention
Typically, high concentrations of anthelmintic compounds are required for killing parasites in their habitat within a host. In the case of intestinal nematodes, anthelmintics must be ingested or absorbed by the worms for expulsion of the parasite from the host. The absorption of the anthelmintic compound by the nematode within the host does not necessarily result in ovicidal activity. Animals being treated are placed in a different pasture or area than before treatment to avoid nematodel ova. There is a need for products which control nematodel ova in the environment of the animal.
This invention relates to a method of controlling nematodes by contacting eggs thereof with a bacterial toxin having ovicidal activity.
2. Description of the Prior Art
Luthy et al. [Pharmacology and Therapeutics 13:257-283 (1981)] teach that various Bacillus species have been recognized as insecticidal pathogens, with B. thuringiensis being the most widely used, commercially available bacterium for insect control. According to Burgess [Parasitology 84:79-117 (1982)] a number of isolates of B. thuringiensis have been reported. Some of the earlier bacterial varieties were active against lepidopteran insects, more recent isolates of B. thuringiensis show activity toward non-lepidopteran insect species. For example, B. t. israelensis is active against dipteran insects, such as mosquito species and blackfly larvae. Other varieties of B. thuringiensis also show promise against mosquito species which play an important role in the transmission of parasitic diseases of man.
Despite the use of microbial species and their products as insecticides, there is not much information available about the microbial control of nematodes. Ciordia et al. [J. Parisitology 47:abstract 41 (1961)] describe the mixing of spores of B. thuringiensis with cow feces that contain eggs of Cooperia punctata, C. oncophora, and Ostertagia ostertagi and recover reduced numbers of third-stage larvae as the concentration of spores per gram of feces increased clearly showing that some strains of B. thuringiensis have nematicidal activity.
Bottjer et al. [Experimental Parisitology 60:239-244 (1985)] teach that a large number of strains of B. thuringiensis and their toxins were effective in killing the ruminant nematode Trichostrongylus colubriformis and other nematodes. All the tested strains of B. thuringiensis were toxic to T. colubriformis eggs.
Tinelli et al. [Federation of European Biochemical Societies Letters Vol. 142:155-158 (1982)] suggest that toxins from Bacillus sphaericus effectively kill mosquito species, particularly Anopheles larvae. Further, Tinelli et al. [CR Acad. Sci. Paris:291/D 537-539 (1980)] describe the technique for the extraction of a crude fraction from B. sphaericus Pasteur 1593 spores, which is highly toxic to An. stephensi larvae.